Conventional pinch valves include a single port for inlet and outlet of control fluid to and from the valve cavity surrounding the flexible sleeve which opens and closes the passageway through the valve. A three-way valve is provided upstream from the port to control the inlet and outlet of fluid to the cavity. In a first position, the three-way control valve allows fluid to flow into the cavity, and thereby close the valve. In a second static position, the control valve is closed so that fluid does not flow to or from the cavity, such that the pinch valve remains closed. In a third position, the control valve exhausts fluid from the cavity, thereby opening the pinch valve. Such a three-way valve is normally more expensive than a two-way valve, and thus increases the cost of the pinch valve.
Pinch valves having dual inlet and outlet ports are also known, although expensive controls are necessary for opening and closing the valve. For example, U.S. Pat. No. 5,549,793 uses a control valve on a inlet opening operated in a pulse width modulated manner to control pressure within the pinch valve cavity, and has an inlet opening and a bleed or leak outlet to release pressure from the pinch valve cavity. The means for varying the diameter of the opening in the U.S. Pat. No. 5,549,793 patent increases the cost of the pinch valve. U.S. Pat. No. 4,454,983 also shows a pinch valve with an inlet opening to the pinch valve cavity and a smaller outlet opening which is controlled by a manual valve to open and close the pinch valve. The smaller outlet opening, as compared to the inlet opening, slows or delays the opening of the pinch valve, since pressure in the cavity is slowly released from the cavity.
Accordingly, a primary objective of the present invention is the provision of an improved pinch valve having separate inlet and outlet openings for controlling opening and closing of the pinch valve.
Another objective of the present invention is the provision of an improved pinch valve having inlet and outlet openings with a fixed diameter, to reduce cost of the pinch valve.
A further objective of the present invention is the provision of an improved pinch valve wherein the inlet opening is smaller than the outlet opening to facilitate opening of the pinch valve.
Another objective of the present invention is the provision of an improved pinch valve having inlet and outlet openings, with a control valve for the outlet opening.
Yet another objective of the present invention is the provision of an improved pinch valve which controls opening and closing of the valve without anemically controlling the fluid flow rate into the pinch valve cavity.
Another objective of the present invention is the provision of an improved pinch valve which controls only the outflow of control fluid from the pinch valve cavity, without controlling the inflow of fluid into the cavity.
Still another objective of the present invention is the provision of an improved pinch valve having a check valve for the control fluid inlet opening to prevent backflow of fluid from the inlet opening.
Another objective of the present invention is the provision of an improved pinch valve which is economical to manufacture and durable and efficient in use.
These and other objectives will become apparent from the following description of the invention.